Quantitation of the Cell-Mediated Immune Response

Abstract Quantitative aspects of the cell-mediated immune response of C57BL mice to a mouse DBA/2 mastocytoma cell have been studied by an in vitro assay involving the cytolytic activity of splenic lymphocytes towards 51Cr labeled target cells. Cytolysis of the DBA/2 mastocytoma cells by “sensitized” C57BL lymphocytes was shown to be a “one-hit” phenomenon, i.e., that lysis of a target cell resulted from single interaction with specifically sensitized “effector” cells. Kinetic studies showed that the rate of target cell destruction fell markedly with time following mixing with lymphocytes, and thus suggested that there is reciprocal death of the interacting cells at least from a functional standpoint, if not morphologically. These findings suggested a means of calculating the number of effector lymphocytes in the splenic pool of sensitized animals, by determining the maximal number of target cells that a given number of lymphocytes could lyse under specified conditions in gross target cell excess. Such determinations were used to compare the effect of mode and dose of antigenic stimulation on the cell-mediated immune response. Optimal antigenic stimulation of C57BL mice with alloantigenic mastocytoma cells was found to be by the intraperitoneal route. Maximal responses were elicited with 107 cells and occurred 11 days following antigenic stimulation. Under these conditions it was estimated that approximately 4% (4 × 104 out of 106) of the lymphocytes were effector cells. Incorporation of the mastocytoma cells into adjuvants (either complete or incomplete Freund's) resulted in a marked diminution of both humoral and cell mediated immune responses. Using complete Freund's adjuvant the maximal number of effector cells produced following antigenic stimulation with 3 × 107 mastocytoma cells was approximately 5 × 103/106 lymphocytes. The number of effector lymphocytes resulting from stimulation with 3 × 107 mastocytoma cells rose exponentially from day 4 (when the cytolytic activity was first demonstrable) and when there were calculated to be 50 effectors/106 lymphocytes to day 11 (4 × 104/106 lymphocytes) and fell therafter. The generation time of the cell population involved in cytolysis was estimated to be approximately 17 hr.